Need some advice on bad geometry from NX Unigraphics  1-20  21-25

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 From:  sneather
5870.1 
I'm receiving some product CAD files from a client. They're using NX Unigraphics, and I have them exporting STEP 203 and 214 files (as I have no idea what the difference is...).
But I'm immediately seeing some areas of bad geometry in MOI. I'm attaching a stripped-down section of just one part, which shows the odd sweep piece, inside a rounded curve. There arr more instances like this, elsewhere. I assume this is happening inside NX, but when the designer looks, he says it looks fine on his end.

So, is this something which is happening when NX is writing the STEP file?

Or is this something that is happening when MOI is reading the STEP file?

Or none of the above? Maybe it is, indeed, just bad geometry, or more specifically the method by which NX simple creates its files? These are real products, which are used to make the tooling and molds for the final pieces. So, I know whatever they are doing in NX, it's working fine for their production.

Anyone have any suggestions?

Thanks!



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 From:  Michael Gibson
5870.2 In reply to 5870.1 
Hi sneather, it's probably happening while MoI is reading the STEP file.

The way NX and also STEP format handles trim curves is a bit different than how MoI handles them - MoI handles trimmed surfaces by a UV space boundary in addition to the 3D edge curves, while NX/STEP can contain only 3D trimming curves. The main difference between these is on surfaces that are closed and have a "seam edge" in them like that particular one. If NX writes out trimming curves for a closed surface where the trimming curve crosses right over the seam edge, MoI has to cut those particular edges up into separate pieces where they cross over the seam (because UV space ends at the seam), and that can be a kind of delicate operation and it's likely to be what is not working quite right on that particular example. It could be exacerbated by things like a trim curve that kind of wavers a bit back and forth across the seam or things like that.

You might try using IGES format instead for a case like this where you've run into a problem - IGES files will often have surfaces in them that are trimmed by UV space curves, and those trim curves can be used directly by MoI's importer rather than needing to be split up at seam crossings. Sometimes IGES files can have different problems though so it's not a bad idea to ask for both STEP and IGES files both and try the other one if you run into a problem.

If there are only a small number of those problem areas, it's possible to manually repair those things by an untrim/retrim operation. To do that, select that face and use Edit > Separate to break it out into its own surface, then select one edge and use Ctrl+A to select all edges of that surface and hit delete to untrim it and recover the full underlying surface. Then use Edit > Trim to trim that surface with the edges of the surrounding pieces and then join the newly trimmed surface back in.

- Michael
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 From:  Michael Gibson
5870.3 In reply to 5870.1 
It's actually kind of hard to know for sure what went wrong without being able to examine the original STEP file and seeing how other programs also behave with it as well.

That one particular area has a trimming boundary that looks like this (note the pretty big gap in one area):



That doesn't quite look like a seam splitting problem, it looks more like bad/inaccurate trimming geometry in the original model, but it's hard to know for sure without going into that area in NX in the original model and examining it though.

Is it possible for you to send the original STEP file before import so I can test it with a couple of other programs to see what they do there?

- Michael

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 From:  Michael T. (MICTU_UTCIM)
5870.4 
Hi sneather and Michael G.

We use NX 8.0 and MoI here at work. We also have a software called 3D Tool. What I usually do is export a Parasolid from NX, convert it to SAT using 3D Tool, then bring it into MoI.

What you could do is have your client send you a Parasolid instead of a STEP file. You can download and install "CAD Exchanger" software and convert the Parasolid to SAT. I say this because the 3D Tool software runs about $900 USD.

This has worked pretty clean for us, but their are always exceptions.

You can also use the "CAD Exchanger" software to send Parasolids back to your client. My experience is that Parasolids back into NX seem to work better than STEP files.

Michael T.
Michael Tuttle a.k.a. mictu http://www.coroflot.com/DesignsByTuttle
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 From:  sneather
5870.5 In reply to 5870.2 
As always, thanks Michael. Great information.

Just to understand the differences and advantages / disadvantages, I'll have them send me both a STEP and and IGES file next time, to test.

As for your prescribed steps to try and fix the bad spots, wow! I wasn't entirely sure what was going to happen, but it worked on the exact example file I posted here. I never realized that there was hidden surface data, under the trim parameters. There is still some weird line data in the new piece I arrived at, but the surface itself looks perfect, and if it looks that way once it gets into C4D, then that problem is solved! And, fortunately, it is only in a few spots on the product they sent. Granted, it could be worse on other ones, but if I can go in and try an fix things, that's one less major concern I would have.

Cheers!

P.S. I forgot. One other question. The scale tat which these products are importing is tiny. When I receive the same kinds of product CAD from one of their affiliates who use ProE, the files seem to import accurately at 1:1 in MOI. The NX guys are using inches, but would that account for such a massive discrepancy? Is there something which I should be doing in MOI to counteract that?
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 From:  Michael Gibson
5870.6 In reply to 5870.1 
Hi sneather, so in order to repair this I drew in this new curve shown here:



Then I did an untrim and a retrim of both of the surfaces to either side of that area that previously had a large gap in the trim boundary, that's how I got the fixed model version which I have attached. Before doing the untrim sometimes you also need to duplicate some edge curves (by selecting then copy/paste) if they are ones you need for retrimming and they are going to get erased by the untrim.

- Michael

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 From:  Michael Gibson
5870.7 In reply to 5870.5 
Hi sneather,

> There is still some weird line data in the new piece I arrived at, but the surface itself looks perfect,
> and if it looks that way once it gets into C4D, then that problem is solved!

If the boundary has got gaps in it like it did here sometimes you may also need to draw in some additional curves and also include those when doing the trimming, in order to make a better formed boundary, check out above for how that looks.


> P.S. I forgot. One other question. The scale tat which these products are importing is tiny. When I
> receive the same kinds of product CAD from one of their affiliates who use ProE, the files seem to
> import accurately at 1:1 in MOI. The NX guys are using inches, but would that account for such a
> massive discrepancy?

Hmmm, I don't really know what would cause this, other than if they're actually modeling things at a tiny scale in NX to start with. If they are doing that it could also explain some of the trim curve problems as well because gaps like the one shown here can sort of be treated as ok (and not refined further or calculated to higher accuracy or things like that) if they're at a very small size.


> Is there something which I should be doing in MOI to counteract that?

Well, you can scale the model, either click on the size line in the properties panel in the upper-right area of the window, or use the Transform > Scale command to scale things up.

But if model data itself happens to be tiny then it will come into MoI tiny initially as well.

You might try testing the STEP file with other programs too, to see if the tiny size is indeed just how the file is set up or whether there is something going on with MoI in particular.

It's hard for me to know for sure what's going on with that without being able to look at the actual STEP file.

- Michael
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 From:  sneather
5870.8 In reply to 5870.4 
Thanks, Michael T.
Great info. I'm Mac based, so my choices for CAD help are rather limited, to say the least. I just checked on CAD Exchanger, per your suggestion, and there is some form of a Mac OS Beta. But I need a license to try it, so I email them that request. So, until then, I'm stuck with getting either the STEP or the IGES files.

Although, do you have any other suggestions regarding little tips or tricks for setting up the files in NX, to help avoid some of these issues down the line? Or is it just inevitable, because the way the STEP files are processed and opened inside MOI, as Michael G. stated?

Thanks.
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 From:  Michael Gibson
5870.9 In reply to 5870.8 
Hi sneather also just a heads up - since we've posted a few messages at the same time here it may have been easy to miss some of them above.

- Michael
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 From:  sneather
5870.10 In reply to 5870.7 
Michael G.
The import scaling is odd. I'll talk to the NX CAD guy again, to see what else he can think of. But like I said, these guys are doing real manufacturing, so somehow things are working out in their pipeline. I could see it being directly on their end, if they were hobbyists, or just doing conceptual work. But I'm a little stuck (being on Mac OS). MOI is my only app for importing STEP, before exporting .OBJ for Cinema. I also have a Rhino Mac Beta, but it specifically does not handle importing STEP files. Which is a real bummer, to say the least.
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 From:  Michael Gibson
5870.11 In reply to 5870.10 
Hi sneather, you could also try ViaCAD for importing the STEP file, I'm pretty sure they have a Mac version. If things behave pretty differently between MoI and ViaCAD for the import then that could mean something needs to be tuned up in MoI. If they behave the same then it's pretty likely to be just how the file is set up.

Is the 3DM file you posted one that is at the import scale that you're talking about or did you scale that up already?

- Michael
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 From:  sneather
5870.12 In reply to 5870.11 
Yes. I forgot about ViaCAD. I'll look into that.

The example file I posted is unaltered in scale. Because I get random changed and updated pieces from my clients, it's crucial that I maintain a consistent set of standards throughout. So if I can avoid having to scale their work up, then it's all the better. That just adds some variables, and as you pointed out, the tiny size can have an impact on how the edges (and gaps) are seen by MOI upon import.

I need to check on the option to send you the original STEP file. Unfortunately, I have certain agreements with the clients, so it may not be possible. I hope you understand.
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 From:  sneather
5870.13 In reply to 5870.11 
By the way. I'm still using MOI v2.52. I suppose there would have been no way for you to know.
Should I definitely be trying the V3 Beta? Might that help with what we're talking about right now...?
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 From:  sneather
5870.14 In reply to 5870.13 
I installed a trial version of ViaCAD Pro Mac, and the original STEP file imports with no obvious geometry defects. So, it does seem to appear that MOI might be having a little harder time with certain STEP files.
However, it did take substantially longer to import into ViaCAD than MOI. But that's not really critical.

The hyper-small scaling issue seems to persist, however. I tried performing a bevel on an edge, and found that I needed to use incredibly small (.001) radii for it to take. Just like what happens in MOI. So, it seems to be an issue on the NX designer's end.
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 From:  Michael Gibson
5870.15 In reply to 5870.13 
Hi sneather,

> By the way. I'm still using MOI v2.52. I suppose there would have been no way for you to know.
> Should I definitely be trying the V3 Beta? Might that help with what we're talking about right now...?

I would generally recommend using the v3 beta to just have the latest stuff. There have been some updates to the STEP import library since v2.52 so it is possible that it could behave better.

It's generally best to run with the v3 beta primarily though.

- Michael
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 From:  Michael Gibson
5870.16 In reply to 5870.14 
Hi sneather,

> I installed a trial version of ViaCAD Pro Mac, and the original STEP file imports with no obvious
> geometry defects. So, it does seem to appear that MOI might be having a little harder time
> with certain STEP files.

Also I think in ViaCAD there are some options for "healing" the file which tries to automatically modify problematic geometry, it could be possible that is actually repairing the problem. That's probably also why it's taking a while for it to process it. It's pretty hard to know for sure without more detailed examination of the STEP file.

ViaCAD also comes in a less expensive version that's just $99: http://www.punchcad.com/p-9-viacad-2d3d-v8.aspx which I'm pretty sure also includes STEP import - it can be a pretty useful tool to add into the mix.


> I need to check on the option to send you the original STEP file. Unfortunately, I have certain
> agreements with the clients, so it may not be possible. I hope you understand.

Certainly, I understand, and please don't do anything to jeopardize the relationship with your clients. Sometimes it can be hard for me to give very much specific additional feedback about file translation issues when the actual files involved can't be shared though.

Also if you need to keep something private you can send it to me through e-mail at moi@moi3d.com instead of posting it here on the forum.

- Michael

EDITED: 1 May 2013 by MICHAEL GIBSON

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 From:  Michael Gibson
5870.17 In reply to 5870.12 
Hi sneather,

> The example file I posted is unaltered in scale.

Ok, but the example file you posted does not seem to be so exceptionally tiny in scale though... the whole piece is about 4 inches in size across, isn't that probably the actual size of the physical object that they're producing?

They've got some pretty small little individual features as part of that model but the overall full object scale does not seem to be so tiny there... ?

- Michael
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 From:  sneather
5870.18 
Good. I'll get going with the V3 beta. I assume that it won't affect my reliable v2.52, right?

With ViaCAD, I did enable the STEP import option to "Stitch Surfaces Into Solid". Perhaps that helped with the dodgy geometry?

And thanks for the email address. I'll see about getting you and intact STEP file for your evaluation purposes.

The import scale is a weird one. I had no idea that it was that size in MOI, and that ~4inches is right in the ballpark. Now things are even more confusing.
My reason for assuming the scales are off, is because I have a set of reliable numbers I use (for instance) for adding small bevels to certain hard edges on the products. I do enough of these products were I can count on those numbers to look right. Normally, I would use something like .1 or .25. Now, that has always worked with the ProE STEP exports I get, and they are the same products as the ones I am also now receiving from NX. But with the NX STEP file, I had to back WAY off to .001 to approximate the same edge profile.
So, I don't know what to do to figure this out.
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 From:  Michael Gibson
5870.19 In reply to 5870.18 
Hi sneather,

> I assume that it won't affect my reliable v2.52, right?

Yeah it should not have any effect on v2.52 .


> With ViaCAD, I did enable the STEP import option to "Stitch Surfaces Into Solid".
> Perhaps that helped with the dodgy geometry?

Hmmm, probably that particular setting doesn't control that. Some other programs based on the same library that ViaCAD uses have options for turning on or off "healing" of the imported geometry. I thought ViaCAD might too but I see it doesn't. Maybe ViaCAD just has that permanently turned on.


> But with the NX STEP file, I had to back WAY off to .001 to approximate
> the same edge profile.
> So, I don't know what to do to figure this out.

I guess I'd need to know more about which specific edge you're trying to bevel in each case to be able to give you more information about this one... Are you sure you're not trying to bevel an edge that is just longer and on the outside of the object in one case but then doing one that is much smaller on some little portion of one of the inside details in the second case?

- Michael
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 From:  BurrMan
5870.20 In reply to 5870.18 
"""""""The import scale is a weird one. I had no idea that it was that size in MOI, and that ~4inches is right in the ballpark. Now things are even more confusing."""""""""""""

You might assume that the NX step file is being written as "MM" instead of inches.
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